The development of renewable energies has been highlighted as a driver of the energy transition towards a more sustainable society. Despite the well-known benefits in health and regional energy resilience when those sources are leveraged, wind- and solar-based technologies bring about flexibility challenges in the power system. The variability in the generation of energy from renewable sources is probably its greatest weakness. This problem can be alleviated in different ways, but a detailed statistical analysis of the situation in each country is necessary to find the optimal solution in each case. This article analyses, from historical data and possible scenarios, some consequences that must be taken into account in the growth of electric power generation with renewable sources. Many assessment reports have been published to analyse high shares of the variable renewable energy supply (VRES) contribution in the electricity mix. This article aims to improve the accuracy in such reports through a novel analysis tool. Hourly timescale and the use of kernel probability distributions allow the well-represented supply and demand profiles necessary for an in-depth insight into electricity management. Spain offers multiple peculiarities which make our native region of interest for research activities. Here, an official report is analysed for three case studies: Spain as an energetic island without storage; Spain as an energetic island with storage; and Spain with both storage and international interconnections. According to this scenario, in 2050, the results indicate an underestimation of VRE generation (19% of renewable overcapacity) leading to very important challenges to the power system operator in the management of situations with 19 consecutive hours of electricity overproduction. In addition, a common output deserves attention: facing such scenarios with very high shares of VRES, more flexibility is required in the power system in order to be efficient in progressive electricity development. Keywords: Variable Renewable Energy (VRE), kernel probabilistic distribution, storage, energy reports, power system analysis